The objective of this work is to develop an improved instrument for monitoring intracranial pressure. Widely acknowledged is the need for a reliable intracranial pressure monitor for patients with head trauma, cerebral edema, hydrocephus, or who have requirements for post-operative intensive care after neurosurgery. There have been many proposals for using electronic means for replacing the older manometric devices for measuring intracranial pressure. Of these approaches, the implanted passive transensor appears to us to be the most promising and worthy of further development. It has a number of distinct advantages for clinical applications. These are 1) Simplicity of the implanted device, 2) No requirements for wire or tubing connections to the device, 3) No requirements for later removal, 4) Long term monitoring over a period of years is feasible, 5) Quality control for assuring long term stability is well within the state of the art. We have overcome a number of technical problems in applying the passive transensor technique and at present have in an animal an implanted transenor which has remained stable over a period of five months. Now that a successful design for a passive transensor has evolved, a number of tasks remain for developing a practical instrument useful for routine clinical applications. These tasks are: 1) Standardization of the fabrication method so that all transensors will operate within narrow limits, 2) Validation tests in animals in which intracranial pressure is precisely known, 3) Development of the external recording and alarm system for use in the intensive care of neurosurgical patients, and finally, 4) Clinical evaluation using selected patients.